1. Field of the Invention
The present invention relates to air intake systems for carburetor-equipped internal combustion engines, and, more particularly, to an air intake system featuring a device for automatically controlling the intake air temperature by means of a continuously adjustable flapper valve which mixes cold raw air with preheated raw air, for the establishment of an optimal raw air intake temperature, under changing operating conditions.
2. Description of the Prior Art
The efficiency of carburetion and combustion in a carburetor-equipped internal combustion engine is highest, when the temperature of the combustion air which is consumed by the engine is maintained within an optimal temperature range. Whereas a higher than optimal air temperature reduces the volumetric efficiency of the engine, a lower than optimal air temperature leads to poor carburetion and, in extreme cases, to carburetor icing, especially under full-load operation.
The intake of cold raw air has the additional disadvantage of delaying the desired rapid warmup of the engine during a cold start. A rapid engine warmup is not only beneficial for the longevity of the engine, by minimizing engine operation in a state of poor lubrication, it is also important for ecological reasons, because the emission of exhaust polutants is higher than normal during engine warmup from a cold start.
It is generally considered impractical to cool a flow of raw intake air whose temperature is above the optimal range, but there exists a readily available, inexpensive source of heat for the purpose of preheating raw intake air whose temperature is below the optimal range. The cold raw air, or a variable portion thereof, is simply drawn through a so-called exhaust stove which is associated with the exhaust manifold of the engine. In the exhaust stove takes place a heat exchange between the hot exhaust gasses and the cold raw air.
A number of flow mixing devices for cold raw air and preheated raw air have already been proposed in the past. The present invention is an outgrowth of a prior invention which is disclosed in U.S. Pat. No. 4,144,857. The background information contained in the latter should be relied upon as background information for the present invention.
The aforementioned U.S. Pat. No. 4,144,857 features a wax thermostat as part of a drive connection between an air flow proportioning flapper valve and a pneumatic valve actuator. It has been found that the absence of a longitudinal adjustability of this drive connection represents a shortcoming in connection with a mass production setup, inasmuch as it necessitates narrow manufacturing tolerances on the constituent parts of the drive connection and on the supporting duct work. The necessary manufacturing accuracy and quality control reflect themselves in higher manufacturing costs and in a greater percentage of rejected parts.